Underestimation of the incidence of new-onset post-coronary artery bypass grafting atrial fibrillation and its impact on 30-day mortality.

OBJECTIVE: Inconsistent definitions of atrial fibrillation after coronary artery bypass grafting have caused uncertainty about its incidence and risk. We examined the extent to which limiting the definition to post-coronary artery bypass grafting atrial fibrillation events requiring treatment underestimates its incidence and impact on 30-day mortality.

METHODS: We assessed in-hospital atrial fibrillation and 30-day mortality in 9268 consecutive patients without preoperative atrial fibrillation who underwent isolated coronary artery bypass grafting at 5 US hospitals (2004-2010). Patients who experienced 1 or more episode of post-coronary artery bypass grafting atrial fibrillation detected via continuous in-hospital electrocardiogram/telemetry monitoring were divided into those for whom Society of Thoracic Surgeons data (applying the definition "atrial fibrillation/flutter requiring treatment") also indicated atrial fibrillation versus those for whom it did not. Risk-adjusted 30-day mortality was compared between these 2 groups and with patients without post-coronary artery bypass grafting atrial fibrillation.

RESULTS: Risk-adjusted incidence of post-coronary artery bypass grafting atrial fibrillation incidence was 33.4% (27.0% recorded in Society of Thoracic Surgeons data, 6.4% missed). Patients with post-coronary artery bypass grafting atrial fibrillation missed by Society of Thoracic Surgeons data had a significantly greater risk of 30-day mortality (odds ratio, 2.08, 95% confidence interval, 1.17-3.69) than those captured. By applying the significant underestimation of post-coronary artery bypass grafting atrial fibrillation incidence we observed (odds ratio [Society of Thoracic Surgeons vs missed], 0.78; 95% confidence interval, 0.72-0.83) to the approximately 150,000 patients undergoing isolated coronary artery bypass grafting in the United States each year estimates this increased risk of mortality is carried by 9600 patients (95% confidence interval, 9420-9780) annually.

CONCLUSIONS: Defining post-coronary artery bypass grafting atrial fibrillation as episodes requiring treatment significantly underestimates incidence and misses patients at a significantly increased risk for mortality. Further research is needed to determine whether this increased risk carries over into long-term outcomes and whether it is mediated by differences in treatment and management.